1. Field of Invention
The present invention relates to a capacitor device. More particularly, the present invention relates to a capacitor multiplier which is suitable for providing large capacitance in an integrated circuit.
2. Description of Related Art
In general circuit designs, capacitor devices of large capacitances are usually required in the circuits. For example, error amplifier and capacitor are usually used in a general circuit for frequency compensation to improve the performance of the circuit. For example, as shown in FIG. 1, the voltage converter 100 includes an integrated circuit (IC) 110, an inductor L11, a load capacitor C11, feedback resistors Rf1, Rf2, a compensating resistor Rz1, and a compensating capacitor Cz1. Since the voltage converter 100 is a typical buck DC-DC voltage converter, the operation detail will not be described here again. Generally speaking, to compensate the low-frequency pole of the voltage converter 100, the capacitance of the compensating capacitor Cz1 has to be very large. Thus, the compensating capacitor Cz1 has to be disposed outside the IC 110.
FIG. 2 is a circuit diagram of a voltage converter which uses another compensating technology. Referring to FIG. 2, the voltage converter 200 includes an IC 210, an inductor L21, a load capacitor C21, a feedback resistor Rf, a compensating resistor Rz2, and compensating capacitors Cz2, Cz3. Here, the voltage converter 200 is a typical buck DC-DC voltage converter, and the operation detail thereof will not be described again. Generally speaking, the capacitance of the compensating capacitor Cz3 is much smaller than the capacitance of the compensating capacitor Cz2. To compensate the frequency appropriately, the capacitance of the capacitor Cz2 has to be very large. Thus, the compensating capacitor Cz2 has to be disposed outside the IC 210.
However, the added compensating capacitors occupy very large circuit area since large capacitances are required. Thus, capacitors used for compensation are generally disposed outside the ICs. Such design will certainly put limit to the present trend of downsizing products. Therefore, product volume and cost can be reduced effectively if the capacitors having large capacitance can be disposed inside the ICs.